1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter, referred to as an "LCD") device for use in a display system and an optical data processing apparatus, a method for producing the same, and a display apparatus using such an LCD device.
2. Description of the Related Art
One of the known LCD cells is a nematic LCD cell which is produced without performing alignment treatment of surfaces of substrates (see Nose et al, Akita University, Department of Electronics, Memory Effects of an Opaque State in a Nematic Liquid Crystal Cell without Rubbing, Lecture Notes on the 18th Conference on Liquid Crystals, pp. 42-43).
Such a type of nematic LCD cell is produced in the following manner. Two substrates each having an electrode thereon are covered with such an alignment film as to realize homogeneous alignment of liquid crystal molecules relative to the substrates. After injecting the liquid crystal molecules between the substrates, the resultant liquid crystal cell is heated until the liquid crystal goes into an isotropic phase. Then, the liquid crystal is cooled down while applying an electric field or a magnetic field which has a level higher than a threshold level for causing Freedericksz transition until the liquid crystal goes into a nematic phase.
The LCD device produced in the above-described manner does not require a polarizing plate. Accordingly, such an LCD device has a high transmittance with respect to visible light, and therefore a light scattering state and a light transmitting state can be switched by a relatively small difference in the potential of the electric field. For example, an image obtained by such an LCD device has a contrast of 4.
Another known nematic LCD device also has an alignment film without being subjected to alignment treatment. To the liquid crystal molecules, a chiral dopant is added to twist the liquid crystal molecules at 90.degree. after being injected between two substrates. Such an LCD device includes polarizing plates (see Stanley Electric Co., Ltd. and Tokyo University of Agriculture and technology, SID '93 DRAFT, pp. 622).
A nematic LCD device without an alignment film includes a Schiff base liquid crystal and has a microscopic region formed therein utilizing the alignment characteristic of the Schiff base liquid crystal (see Japanese Patent Publication No. 45-12839).
The above-described LCD devices have the following problems.
The LCD device having the liquid crystal molecules in the state of homogeneous alignment between two substrates display images utilizing the difference in light transmittance between a light scattering state and a light transmitting state. However, the light transmittance in the light scattering state cannot be very low. Accordingly, in the case that light incident on the LCD device is not parallel light, the contrast of an image obtained by the LCD device is extremely low. For such an inconvenience, such an LCD device can hardly be used as a direct-view liquid display device.
The LCD device including the liquid crystal molecules mixed with a chiral dopant exhibits hysteresis in that it has different levels of light transmittance even though an identical voltage is applied, depending on whether the voltage is obtained by increasing the voltage or decreasing the voltage. Further, satisfactory display is not obtained due to remaining images caused by hysteresis.
The LCD device including the microscopic region can only use limited types of liquid crystal materials such as p,n-aminobenzylidene, p'-aminobenzonitrile, p,n-octoxybenzylidene, and p'-octoxybenzonitrile. Since these liquid crystal materials are low in resistance to water and easy to dissolve, a special sealing device such as a glass frit seal is necessary. Sealing should be performed at a temperature of approximately 500.degree. C. Such a high temperature increases a resistance of a transparent electrode or deteriorates the characteristics of a nonlinear device used in the LCD device. For these reasons, this type of LCD device is not currently used widely.